Exciting developments in doppler ultrasound have demonstrated that many vascular diseases can be distinguished by characteristic blood flow patterns. These include carotid artery disease, peripheral vascular disease, cardiac valve stenosis and regurgitation, aneurysms, A-V shunts, and portal vein abnormalities. However, many vessels of interest are not accessible to ultrasound or show poor reproducibility. Although a number of MR imaging techniques have been developed which overcome many of the limitations of ultrasound, there is at present no standard procedure for measuring flow velocities using MRl. The Pl has developed a novel MR imaging sequence that slice-selectively inverts longitudinal magnetization thereby tagging consecutive boli of material as they enter the selected slice. This technique provides a method for quantitating flow velocities that has many attractive features. The specificity and sensitivity of the bolus tagging technique and conventional MR flow quantitation techniques will be examined to determine the method most suitable for velocity quantitation. This will be accomplished by: Simulating the flow patterns and magnetization distribution for steady and pulsatile flow through regular and irregular vessels in response to velocity quantitation pulse sequences. Conducting phantom studies with accurately controlled flow phantoms to validate the conclusions of the simulation studies. Demonstrating the viability of these sequences in studies on human volunteers. 3D display strategies and thick-slab multi-slice methods will be used to derive quantitative measures of velocity for material moving through tortuous vessels. Measures of the velocity at multiple points in the pulsatile cycle where either the cycle period is not known a priori or where the flow amplitude may vary from cycle to cycle will be obtained with post-hoc rebinding methods. Methods to determine the presence of turbulent flow a to distinguish between the various contributions to intra-voxel mixing and signal loss in disturbed flow will be examined. The significance of this project is that, in clinical studies, this will provide the capability to noninvasively determine the dynamic and spatial variation of the velocity of blood flow (and thus total blood flow) through the body vessels. Those quantities could then be related to the disease state of the vessel and would aid in the diagnosis and treatment of flow-related dysfunction.